1. Field of the Invention
The present invention relates to a backup ring and more particularly to a backup ring having a convex shape and/or cantilever portion for providing a controlled space between the backup ring and a relatively moving part when in a pressurized state.
2. Description of the Related Art
Sealing devices between two relatively moving parts are well known in the art. When the two moving parts include a shaft and a concentric housing, the sealing device typically comprises a first annular seal ring, and an energizer ring working in combination with the seal. Both the seal ring and the energizer ring are typically disposed in a gland or a groove carved into the housing, and face the rotatable shaft to form a sealing relationship with the shaft. Some sealing arrangements provide for only a seal to be used as the sealing device. However, if both a seal ring and an energizer ring are used, the seal ring is generally disposed adjacent the rotatable shaft, and the energizer ring disposed along the opposing bottom of the gland or groove.
Often, a seal ring serves to retain lubrication fluid on one side of the seal, preventing the leakage of that fluid even in pressurized states. However, under operation, and especially when high-pressure fluids are involved, a seal ring has a potential to extrude from its position in the gland. This condition, known as a seal blow-out, can halt the operation of the shaft, damage the shaft and housing, and proximately cause significant secondary damage, depending on the application of the shaft and housing.
In part to alleviate the potential for seal extrusion, a backup ring is utilized in many sealing device applications in the art. The backup ring is disposed along the gland wall that carries the seal device during operation. It is common during operation, especially in high-pressure fluid applications, for a seal to shift toward one side of the gland, thereby exerting most of its lateral pressure on a wall of the gland. It is at this time that the potential for seal extrusion is highest.
Placing a backup ring between the sealing device and that gland wall provides a means for further securing the sealing device inside the gland. This is accomplished by providing a seal ring having a concentric annular hole that is either sized to fit around the diameter of the rotating shaft, or it is slightly larger. Physical properties such as elastomeric properties and design tolerances allow the backup ring to substantially prevent seal failure and seal extrusion.
However, it is a potential disadvantage of current backup rings that when a shaft-contacting backup ring is utilized, the system is subjected to additional friction due to the contact between the shaft and the backup ring.
Alternatively, when radially spaced backup rings are used, less protection against seal extrusion is provided, and a means must be implemented in order to engage the backup ring with the shaft thereby preventing fluid leakage. Furthermore, due to varying design tolerances and varying pressures within a pressurized system, an optimal clearance between the backup ring and the shaft is not always consistently achieved.
The present invention pertains to a seal arrangement for sealing a gap between two relatively moving parts, such as a shaft and a housing that is concentric with the shaft. While the following descriptions pertain to a shaft relatively moving within a housing, the present invention is not limited by such an embodiment, and other configurations for two relatively moving parts are within the scope of this disclosure.
A seal arrangement is typically comprised of a primary seal apparatus that is disposed within a gland located between the shaft and the housing, and a backup ring that is disposed between the primary seal apparatus and a wall of the gland. It should be noted that while the following description discloses a preferred embodiment having a gland defined within the housing, it is within the scope of the present invention to have a gland defined in the shaft, wherein the primary seal apparatus and backup ring face the housing and form a sealing relationship therebetween.
The present invention, in one form thereof, comprises a backup ring for providing auxiliary sealing to a primary seal arrangement disposed between a first member having a first contact surface and a second member having a second contact surface, the backup ring comprises a washer shaped member having a perimeter in contact with the first contact surface, the washer having a convexly shaped portion. According to the invention, the convex shape is deflected when subjected to pressure, such that it extends the member into a more linear shape or otherwise changes its shape in a controlled manner, thereby either closing out or opening the seal clearance to a desired gap.
The present invention, in another embodiment thereof, further comprises a generally arcuate cantilever portion extending from the perimeter of the washer. As disclosed in the invention, the cantilever portion extends at an angle from the plane defined by the washer during an unpressurized state, and when pressurized, deforms into a position disposed between a surface of the gland and the primary seal arrangement such that the cantilever portion extends substantially perpendicularly from the plane defined by the washer.
The present invention, in another form thereof, comprises a seal arrangement for sealing a gap between a shaft and a housing, the seal arrangement having a pressurized state and a non-pressurized state, the seal arrangement comprising a primary seal apparatus disposed within a gland between the shaft and the housing, and a backup ring disposed between the primary seal apparatus and a wall of the gland, the backup ring extending substantially radially between the shaft and a gland bottom, and having a convex portion in the non-pressurized state.
The present invention, in yet another form thereof, comprises a method of sealing and gap between a first member and a second member comprising the steps of: providing a primary seal arrangement disposed between the first member and the second member, and providing a backup ring disposed between the first member and the second member adjacent to the primary seal arrangement, the backup ring having a convexly shaped portion that deflects when subject to compressive forces.
The present invention, in a further embodiment thereof, comprises a backup ring disposed between a first member having a first contact surface and a second member having a second contact surface, the backup ring comprising a washer having a cantilever portion extending from the washer at an angle from a plane substantially defined by the washer. According to this embodiment of the invention, the cantilever portion extends at an angle from the plane substantially defined by the washer when the system is in an non-pressurized state, and is deformed into a configuration wherein the cantilever portion extends substantially perpendicularly from the plane defined by the washer in a pressurized state.
During an unpressurized state of the present invention, a primary seal apparatus contacts the shaft on an inner surface of the seal apparatus, and contacts the gland bottom on an outer surface of the said apparatus. The primary seal apparatus may only include a seal ring, or it may include a seal ring and an energizer, the energizer circumscribing the seal ring. In either case, the backup ring is placed adjacent the seal arrangement, such that it is disposed between the primary seal apparatus and a gland wall, on a non-pressurized side of the primary seal apparatus.
In one embodiment of the present invention, the backup ring maintains a convex shape during a non-pressurized state, while being radially spaced from the outer surface of the shaft. However, during a pressurized state, the primary seal apparatus exerts pressure on the backup ring in an axial direction, thereby deforming and radially elongating the backup ring, and consequently encouraging the inner surface of the backup ring to move closer to the shaft. Depending on the application, the backup ring can be designed to engage and seal the shaft during a pressurized state, or provide an optimal clearance between the shaft and the backup ring during the pressurized state.
It is an advantage of the present invention that the backup ring, in one form thereof, provides a substantially frictionless convex shaped design during periods of low pressure operation and provides a selectable positioning with relation to the shaft during a high-pressure state, when the likelihood of seal failure or extrusion is greatest.
It is a further advantage of the present invention, in one form thereof, that the wear on the backup ring during normal operation is greatly reduced because of the clearance provided between the shaft and the backup ring when it is in its convex shape.
It is a further advantage of one embodiment of the present invention that extrusion of the primary seal apparatus and the backup ring is further minimized by the providing a consistently achievable clearance between the backup ring and the shaft.
Yet another advantage of this embodiment is that the axially protruding lip portion provides for a lifting of the backup ring from the shaft, thereby reducing friction and wear.